Device for determining the relative position of a plurality of catheters in the human body
Device for determining the relative position of two or more catheters in the human body, there being disposed on each catheter (4, 5), preferably in the area of the catheter tip, at least one measuring electrode (ME1-ME8; ME9, ME10) which can be connected to a voltage source together with one or more measuring electrodes of a further catheter, wherein the resistance between the measuring electrodes, and hence the distance of the measuring electrodes, can be determined via a current measurement.
This application claims priority to the German application No. 10 2004 030 834.9, filed Jun. 25, 2004 which is incorporated by reference herein in its entirety.
FIELD OF INVENTIONThe invention relates to a device for determining a relative position of catheters inserted into a human body.
BACKGROUND OF INVENTIONIn cardiology, more particularly electrophysiology, two or more catheters are introduced through the vascular system into the heart in order to carry out diagnosis and/or therapy therein. Since relatively large spaces are present in the heart compared to the vessels, the problem arises of navigating the catheters accurately to the desired destination in these spaces and to keep track of their location. In certain cases it is necessary to determine the exact position of a catheter in the space with absolute precision, for example in order to use said position for imaging representations.
SUMMARY OF INVENTIONUntil now, a method measuring absolutely in the 3D space has been used in order to determine the positions of intracardiac catheters relative to one another. Thus, for example, Biosense Webster's Carto positioning system uses an electromagnetic field in which catheters equipped with coils are moved. It is complicated, time-consuming and expensive to set up, calibrate and operate said system. However, systems measuring absolutely are by no means essential for those cases in which only the position of two or more catheters relative to one another is required, in other words, for example, for electrophysiological examinations using what is known as a lasso catheter, with the result that the high technical and financial outlay is not justified.
An object of the invention is therefore to create a device for determining the relative position of two or more catheters in the human body, said device being simple in design and easy to operate so that it can be used without difficulty by anyone with the ability to carry out investigations by means of catheters in the human body.
This object is achieved by the claims.
Since the blood in which the catheters are located is electrically conducting, a current flows between the measuring electrodes. A resistance is calculated from the known voltage and the measured current. The resistance is proportional to the volume of blood that the current has flown through, in other words, therefore, the distance between the two electrodes. Moreover, blood can vary slightly in terms of its composition and consequently the conductivity can also increase or decrease. However, as said variations are minor and there is a constant strong bloodstream in the heart, the variations will barely register given appropriate averaging. For illustration purposes it should be pointed out that while the body is at rest approx. 4-5 liters of blood per minute flow constantly through the atria and ventricles.
In order to avoid disruptions to the current measurement due to signals generated in the body itself or to external electrical signals, an alternating voltage having a specific phase and frequency is preferably applied to the electrodes. The current flowing through the electrodes is measured on a phase—and frequency-selective basis, so only the applied voltage is taken into account in the calculation of the resistance and other voltages are largely suppressed.
A measuring electrode in one catheter will be closer to a measuring electrode of the other catheter than another measuring electrode, which means that the resistance of the blood between the dynamically connected pair of electrodes is therefore greater in the first case than in the second case. By systematic switching of the voltage between all possible pairings of the measuring electrodes of the different catheters with the aid of a control unit, or alternatively by applying voltages of different frequency or at least of different frequency coding to the different electrode pairings, it is thus possible to deduce the spatial position of one catheter relative to the other catheter.
The distance and the relative position can be fed back to the user via pitch coding, for example. Thus, the sound could be at its deepest (or softest) when the distance from the electrode on one catheter to all the electrodes on the other catheter is at its smallest. In another switchable mode the desired position at the edge of the second catheter can be indicated by corresponding sound coding.
In a development of the invention a calibration and calculation of the absolute distance can be performed if the voltage is applied between two measuring electrodes of one catheter that have a known distance relative to one another. Since the material of the catheter itself insulates, only the conductivity of the blood can determine the resistance. Thus, the ratio of length of the current path in the blood and distance can be determined.
In this way the feedback to the user (e.g. by means of pitch coding) can be effected with even greater precision. By means of a pictogram it is possible, taking into account the relativity of the measurement in relation to the position of the heart, to represent the absolute position and distance of the catheters relative to one another.
With particular advantage one of the catheters can be what is known as a lasso catheter, that is to say a catheter having a ring -shaped configuration at the end, which, after being introduced into the cardiac ventricle, deforms into this annular shape due to the elastic property of the material, whereby with such a lasso catheter a plurality of measuring electrodes disposed equidistantly in a distributed arrangement around the loop can be provided, while the second catheter can be an intervention catheter, in particular an ablation catheter.
A lasso catheter of said type is introduced into the junction of a large vessel which leads into the cardiac ventricle (pulmonary vein) and even without use of a navigation system is equipped with a number of electrodes for deriving intracardiac potential s. Owing to the ring shape, that is to say on account of the loop which forms at the front end, it is possible to deduce the position and direction of the potentials in the vessel toward the heart. The straight intervention catheter can be navigated precisely to these sites of potential derivation by the electrophysiologist with the aid of the lasso catheter in order possibly to ablate aberrant conduction pathways with current. In an embodiment of the invention the electrodes which are required in any case for electrophysiological purposes can be used at the same time for the purposes of navigation and determination of the relative position of the catheters; in other words, the electrodes of the catheters for the electrophysiology can also simultaneously be the measuring electrodes. It would also, of course, be possible to use separate electrodes as measuring electrodes.
BRIEF DESCRIPTION OF THE DRAWINGSFurther advantages, features and details of the invention will emerge from the following description of an exemplary embodiment as well as with reference to the drawings, in which:
The reference numeral 1 in
At its front end the lasso catheter 4 has a loop 6 which forms in the heart owing to the elastic property of the material and which is equipped with a plurality of measuring electrodes ME1 to ME8. In the same way two measuring electrodes are likewise arranged at the front end of the straight intervention catheter. The measuring electrodes ME1 to ME8 are the electrodes on the lasso catheter which are required in any case for electrophysiological purposes and are used as well solely for the inventive device for determining the relative position of the two catheters. In a similar manner the electrode ME9 on the straight catheter is the intervention electrode for ablating the aberrant conduction pathways in the junction aperture of the pulmonary vein and only the electrode ME10, which otherwise is by no means absolutely essential for normal application cases, would represent an additional electrode which is required only for the inventive device for determining the relative position of the catheters.
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Claims
1-8. (canceled)
9. A device for determining the relative position of a first and second catheter in a human body, comprising:
- a first measuring electrode arranged on the first catheter;
- a second measuring electrode arranged on the second catheter, the first and second measuring electrodes configured to be connected to a power supply unit, the power supply unit configured to be connected to at least a third measuring electrode of a third catheter; and
- a measuring unit for determining an electrical resistance between the first and second electrodes by measuring an electrical current flowing through the first and second electrodes and for determining a distance between the electrodes based on the determined electrical resistance, wherein the relative position is determined using the determined distance.
10. The device as claimed in claim 9, wherein the first and second electrodes are arranged at a tip of the first respectively second catheter.
11. The device as claimed in claim 9, wherein the power supply unit includes at least a first and a second alternating voltage power supply having different frequencies, and the electrical current is measured by a current measuring instrument configured to measure such currents having a specific frequency and/or a specific phase.
12. The device as claimed in claim 9, wherein the first electrode has a known distance from the second electrode, the power supply unit is connected to the first and second electrodes, and the electrical current is measured for calibrating the measuring unit with regard to absolute distances derived from the current measuring.
13. The device as claimed in claim 9, wherein the first or the second catheter is a lasso catheter having a number of measuring electrodes arranged equidistantly on and distributed over a loop of the lasso catheter.
14. The device as claimed in claim 9, wherein the first or the second catheter is an intervention catheter.
15. The device as claimed in claim 14, wherein the intervention catheter is an ablation catheter.
16. The device as claimed in claim 9, wherein the measuring unit is configured to output the determined distance and relative position to a user of the device using an acoustical signal having a signal frequency related to the determined distance and/or relative position.
17. The device as claimed in claim 9, wherein the measuring unit is configured to output the determined distance and relative position to a user of the device using a pictogram.
18. The device as claimed in claim 9, wherein the first or second electrode is included in a working electrode of the first respectively second catheter, the working electrode configured to execute a medical examination and/or treatment procedure.
Type: Application
Filed: Jun 23, 2005
Publication Date: Jan 12, 2006
Patent Grant number: 7792564
Inventors: Jan Boese (Eckental), Martin Kleen (Furth), Norbert Rahn (Forchheim)
Application Number: 11/165,098
International Classification: A61B 18/04 (20060101);